This invention relates to an apparatus for use in a multi-cylinder internal combustion engine for controlling fuel injection thereto and, more particularly, to a fuel injection control apparatus in which acceleration enrichment is provided in response to a sensed demand for engine acceleration.
During rapid throttle opening maneuvers, lean air-fuel ratio excursions in the mixture drawn into the cylinders will typically result if the fuel supply rate is not increased beyond the normal steady state running fuel requirements. This is the case where the fuel injection period is determined based mainly on the measurement of the intake air flow sensed by an airflow sensor provided to sense the air flow through the engine induction passage.
One reason for the lean air-fuel ratio excursion is that the airflow sensor has a slow response to a rapid air increase resulting from the rapid throttle opening and the signal from the airflow sensor will lag somewhat behined the actual amount of air to the intake mainfold, resulting in a lean air-fuel ratio excursion that may result in degraded engine accelerating performance and emissions.
The lean air-fuel ratio excursion resulting from the slow response of the airflow sensor may be avoided by providing an asynchronous fuel injection in response to a rapid throttle opening representing a demand for engine acceleration. However, this method cannot be applied directly to the fuel injection control apparatus in which fuel is injected in synchronism with engine crankshaft rotation into the engine intake manifold and drawn into each cylinder during its cylinder intake event since the asynchronous fuel injection is required to have a period dependent upon the cranksahft position at which the acceleration demand occurs with respect to the crankshaft position at which a synchronous fuel injection is produced in order to achieve an appropriate air-fuel ratio for all of the cylinders. For example, the asynchronous fuel injection is required to have a greater period when it is made just before or after a synchronous fuel injection than is required when the acceleration demand occurs neither just before nor just after the synchronous fuel injection. It is proposed in Japanese Patent Laid Open No. 59-51137 to determine the period of the asynchronous fuel injection in accordance with the crankshaft position at which the acceleration demand occurs with respect to the crankshaft position at which a synchronous fuel injection occurs. However, such a conventional apparatus fails to achieve an appropriate air-fuel ratio for all of the cylinders. In addition, the conventional apparatus requires a complex device capable of providing an accurate measurement of the crankshaft position at which the period of the asynchronous fuel injection is changed.